Butterfly Nebula (M 2-9)

The Butterfly Nebula (M 2-9) is a planetary nebula with a
dramatic bipolar structure; it lies 2,100 light-years away in the constellation Ophiuchus and was discovered by Rudolph Minkowski in 1947. Many of the unusual features of the Butterfly can be understood
in terms of the central star, which is a close, mass-exchanging binary system,
like a Z Andromedae star (or symbiotic
nova). One of the stars is pulling matter off its partner and spinning it
into a giant disk, about 10 times the diameter of Pluto's
orbit. Hydrodynamic models of the type used to design jet engines show that
such a disk can successfully account for the jet-exhaust-like appearance
of M2-9. The high-speed wind from one of the stars rams into the surrounding
disk, which serves as a nozzle. The wind is deflected in a perpendicular
direction and forms the pair of jets seen in the nebula's image. This is
much the same process that takes place in a jet engine: the burning and
expanding gases are deflected by the engine walls through a nozzle to form
long, collimated jets of hot air at high speeds.